In maxillofacial surgery, the skull and dentition is surgically remodeled or restored. This surgical discipline encompasses surgical interventions of repair, in particular, of a mis-positioning of the jaws with respect to one another, called orthognathic surgery. Typically, orthognathic surgery involves osteotomies of the maxilla and/or mandible to reposition these bone fragments correctly with respect to the rest of the skull and to create a good occlusion. Osteotomies are surgical operations whereby a bone is cut to shorten, lengthen or change its alignments. With ‘occlusion’ is meant the manner in which the teeth from upper and lower arches come together when the mouth is closed.
Today's procedure to prepare orthognathic surgery mainly consists of the following steps:                1. Acquisition of 2D cephalograms and performing measurements on them (the latter process is called ‘tracing the 2D cephalogram’),        2. Measuring critical distances directly on the patient's face,        3. Taking impressions of the upper and lower dental arch in order to produce plaster casts of the dentition. Taking a wax bite registration in order to relate the plaster casts of the upper and lower dentition in order to know the actual occlusion of the patient and to install the casts in an articulator,        4. Based on the results of step 1 and 2, and on additional information derived of a clinical evaluation of the patient, the plaster models are repositioned in order to optimize the occlusion. The plaster models might be cut during this step.        5. A new facial lateral profile is estimated and drawn on top of the traced 2D cephalogram.        6. An acrylic surgical splint is manually created in order to be able to do the same repositioning of the dental arches during surgery.        
With the emergence of 3D technologies, methods to carry out the measurement virtually in three dimensions have been established. As a data input, single or multi-slice CT scans were originally applied. With the emergence of cone-beam CT imaging (CBCT) for dental application, acquisition of 3D scan data becomes common sense in the field.
However, no system is available that visualizes the dentition of the patient in a detailed way using a protocol that is clinically feasible without distorting the facial soft tissues. Such a system would allow detailed occlusion planning possibly even including prediction of soft tissue implication and offer the possibilities to create intra-operative tools to establish the planned solution and to maintain it postoperatively.
WO 2006/000063 describes a method to perform a 3D cephalometric analysis of hard and soft tissues and to derive anatomically relevant movements to reposition bone fragments. It also mentions the possibility to enhance the visualization by fusing a scan of plaster models on the basis of a 3D splint with equipped with at least four markers. An important drawback of said approach is that the 3D splint always disturbs the facial profile.
WO 03/028577 describes a method to generate a surgical splint. The key component in this method is the usage of some markers relative to the patient's dentition identifiable in both the digital dental computer model and the computed tomography computer model to visualize the patient's dentition in detail. The registration method is based on point-based matching. However, this method has as fundamental drawback that the markers are disturbing the natural facial expression during the patient scan. This method to create a visualization of the dentition can be seen as a straightforward extension of the work in the field of dental implant planning (see e.g. ‘An image-guided planning system for endosseous oral implants’, Verstreken et al., IEEE Trans Med Imaging 1998, 17, pp. 842-852).
U.S. Pat. No. 6,152,731 describes a method for using digital dental models in a digital articulator. It is a digital analogue for the traditional articulator with plaster dental casts. However, this method has as fundamental drawback that the relationship with the anatomy of the patient's head is lost since only the teeth are visible.